U.S. patent number 7,140,824 [Application Number 10/699,948] was granted by the patent office on 2006-11-28 for tensioning hydraulic nuts.
This patent grant is currently assigned to Curtiss-Wright Flow Control Corporation. Invention is credited to John Wentworth Bucknell.
United States Patent |
7,140,824 |
Bucknell |
November 28, 2006 |
**Please see images for:
( Certificate of Correction ) ** |
Tensioning hydraulic nuts
Abstract
A hydraulic tensioning system for nuts on studbolts has a puller
bar and a puller buddy, which are coupled to the studbolt, and a
bridge around the nut. The puller bar is internally coupled to the
studbolt (and may engage the nut before the tension is applied).
The nut can comprise a cone nut, which cooperates with a
complementary collar or shell with a conical inner face and a
spherical base washer.
Inventors: |
Bucknell; John Wentworth
(Indooroopilly, AU) |
Assignee: |
Curtiss-Wright Flow Control
Corporation (Falls Church, VA)
|
Family
ID: |
3813105 |
Appl.
No.: |
10/699,948 |
Filed: |
November 3, 2003 |
Prior Publication Data
|
|
|
|
Document
Identifier |
Publication Date |
|
US 20040165963 A1 |
Aug 26, 2004 |
|
Related U.S. Patent Documents
|
|
|
|
|
|
|
Application
Number |
Filing Date |
Patent Number |
Issue Date |
|
|
09914346 |
|
|
|
|
|
PCT/AU00/00138 |
Feb 28, 2000 |
|
|
|
|
Current U.S.
Class: |
411/14.5; 411/19;
411/14 |
Current CPC
Class: |
B25B
29/02 (20130101) |
Current International
Class: |
F16B
31/00 (20060101); F16B 31/04 (20060101) |
Field of
Search: |
;411/14,14.5,19,994,434,915-917 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
|
|
|
|
|
|
|
0 748 671 |
|
Dec 1996 |
|
EP |
|
0 797 012 |
|
Sep 1997 |
|
EP |
|
0797012 |
|
Sep 1997 |
|
GB |
|
Primary Examiner: Sandy; Robert J.
Assistant Examiner: Sharp; Jeffrey A.
Attorney, Agent or Firm: Pearne & Gordon LLP
Parent Case Text
This application is a continuation of application Ser. No.
09/914,346, filed Aug. 27, 2001, and now abandoned, which claims
priority under 35 USC 371 from International Application Serial
Number PCT/AU00/00138, filed Feb. 28, 2000, and Australian
Application Serial Number PP 8905, filed Feb. 26, 1999.
Claims
What is claimed is:
1. A hydraulic tensioner for use in a high tensile force
environment where space is limited, said tensioner applying tension
to a studbolt extending from an article, said tensioner comprising:
a puller bar having a threaded end for threaded engagement with a
threaded end of the studbolt; hydraulic means for exerting a
pulling force on the puller bar and thus the studbolt to apply
tension to the studbolt; a cone nut assembly for fitment to the
studbolt in a position adjacent the article, said cone nut assembly
comprising a nut body for threaded engagement on said studbolt and
having a downwardly and inwardly substantially conical or tapered
peripheral outer surface, and an outer annular collar radially
surrounding said nut body with a complementary conical or tapered
recess to receive most of the nut body, in use; and a bridge for
extending around and over the nut body, operable to react between
the hydraulic means and the article to tension the studbolt by a
pulling force exerted by said hydraulic means on said puller bar to
pull said end of the studbolt in a direction away from the article,
said nut body being adjustable on the studbolt and against the
tapered recess in the outer annular collar to take up elongation of
the studbolt as a result of applying tension to it; wherein, said
bridge stands directly upon said outer annular collar in
operation.
2. A hydraulic tensioner as claimed in claim 1, wherein: the
threaded end of the studbolt includes an internal thread; and the
internal thread in the studbolt is stepped in diameter and the
puller bar has a threaded end with complementary stepped external
threads.
3. A hydraulic tensioner as claimed in claim 1, wherein: the bridge
is engaged between the hydraulic means and the outer annular
collar.
4. A washer for use between the cone nut assembly and article in
the tensioner as claimed in claim 1, said washer comprising: a
first annular means and second annular means mating at a slip plane
angled from a plane transverse to the axis of the washer; and
removable or releasable means holding the first and second annular
means against relative slip over the slip plane therebetween while
the removable or releasable means is in place.
5. A hydraulic tensioner as claimed in claim 1, and further
including: a puller buddy engageable with said threaded end of the
studbolt and engageable with the puller bar so that when the puller
bar is moved to tension the studbolt, the puller buddy is also
moved to tension the studbolt.
6. A coupling for the hydraulic tensioner of the type as claimed in
claim 5 wherein: the threaded end of the studbolt is an internal
thread, and the threaded end of the puller bar is an external
thread; and the internal thread on the studbolt and the externally
threaded end of the puller bar are tapered, and comprise buttress
threads.
7. A hydraulic tensioner as claimed in claim 1, wherein: the
threaded end of the studbolt includes an internal thread; the
internal thread in the studbolt is substantially conical or
tapered; and the threaded end of the puller bar has a complementary
substantially conical or tapered external thread.
8. A coupling for the hydraulic tensioner of the type as claimed in
claim 7 wherein: the internal thread on the studbolt and the
external thread on the end of the puller bar are buttress
threads.
9. A hydraulic tensioner as claimed in claim 7 wherein: the
internal thread on the studbolt and the externally threaded end of
the puller bar are equally tapered, and the threads comprise
buttress threads.
10. A hydraulic tensioner as claimed in claim 9 wherein: the taper
of the internal thread on the studbolt and the taper of the
externally threaded end of the puller bar are at an angle of
approximately 10.degree. to the normal to the horizontal axes of
the studbolt and puller bar.
11. A hydraulic tensioner as claimed in claim 10 wherein: the pitch
of the external thread on the puller bar is greater than the pitch
of the internal thread in the studbolt.
12. A hydraulic tensioner as claimed in claim 11 wherein: the pitch
of the external thread on the puller bar is 100.1% to 100.5% of the
pitch of the mating thread in the studbolt.
13. A washer for use with the tensioner as claimed in claim 12,
said washer comprising: a first and second annular means mating at
a slip plane angled from the plane transverse to the axis of the
washer; and removable or releasable means holding the first and
second annular means against relative slip over the slip plane
therebetween whilst the removable or releasable means is in
place.
14. A coupling within a hydraulic tensioner for applying tension to
a studbolt extending from an article and fitted with a nut and an
outer annular collar radially surrounding said nut, wherein said
tensioner comprises a puller bar for engagement with an end of the
studbolt, hydraulic means acting between the puller bar and the
article and operable to cause the puller bar to tension the
studbolt by pulling said end of the studbolt in a direction away
from the article, and a bridge extending around and over the nut
for transmitting reactive force from the hydraulic means to the
article, said bridge standing directly upon said outer annular
collar, and wherein said coupling comprises: an internally threaded
bore in an end of the studbolt and a complimentary externally
threaded end on the puller bar, said internally threaded bore and
said externally threaded end being tapered at an angle of about
10.degree. to a length axis of the studbolt, and said threads being
substantially uniform and constant throughout their length and
comprising buttress threads having a flank or shoulder facing away
from the article and substantially perpendicular to the common axes
of the studbolt and puller bar and a flank or face facing toward
the article and oriented at an angle of about 45.degree. to the
length axis of the studbolt.
15. A washer for use between the nut and article in the tensioner
as claimed in claim 14, said washer comprising: a first and second
annular means mating at a slip plane angled from the plane
transverse to the axis of the washer; and removable or releasable
means holding the first and second annular means against relative
slip over the slip plane therebetween whilst the removable or
releasable means is in place.
16. A coupling as claimed in claim 14 wherein: the pitch of the
external thread on the puller bar is greater than the pitch of the
internal thread in the studbolt.
17. A coupling as claimed in claim 16 wherein: the pitch of the
external thread on the puller bar is 100.1% to 100.5% of the pitch
of the mating thread in the studbolt.
18. A nut assembly for use with the coupling claimed in claim 14,
the nut assembly comprising: a nut body with a substantially
conical or tapered peripheral outer surface; an annular collar with
a complementary conical or tapered recess to receive the nut body,
in use; and the nut body being screwed, in use, on the studbolt
into the recess of the annular collar.
19. A nut assembly as claimed in claim 18 and further including: a
base washer interposed between the annular collar and the article
and having a substantially part-spherical face engageable by a
complementary part-spherical face on the annular collar to enable
the base washer and annular collar to be self-aligning.
20. A hydraulic tensioner for application with a stud bolt
extending from an article and fitted with a cone nut and an outer
annular collar radially surrounding said cone nut, said tensioner
comprising: a puller bar having a longitudinal axis and a tapered
end tapered at an angle of about 10.degree. to said longitudinal
axis, said tapered end having an external thread for engagement in
an internal thread in an end of the studbolt, said external and
internal threads comprising buttress threads having a shoulder or
flank lying substantially perpendicular to the longitudinal axis of
the puller bar; a puller buddy having an internally threaded end
for engagement with an external thread on said end of the studbolt,
and means on the puller bar for exerting a pulling force on the
puller buddy when a pulling force is exerted on the puller bar; and
an hydraulic means acting between the puller bar and the article
via a bridge positioned around and over said cone nut and against
the puller bar to pull the puller bar and puller buddy in a
direction away from the article to tension the studbolt; wherein,
said bridge stands directly upon said outer annular collar in
operation.
21. An hydraulic tensioner as claimed in claim 20, wherein: the
pitch of the external thread on the puller bar is greater than the
pitch of the internal thread in the end of the studbolt.
22. An hydraulic tensioner as claimed in claim 21, wherein: the
pitch of the external thread on the puller bar is 3.005 mm and the
pitch of the thread in the end of the studbolt is 3.00 mm.
23. A cone nut assembly within a hydraulic tensioner for applying
tension to a studbolt extending from an article, wherein the
tensioner includes a puller bar for connection with an end of the
studbolt, and an hydraulic means acting via a bridge between the
puller bar and article to exert a pulling force on the studbolt in
a direction away from the article, said cone nut assembly
comprising: a cone nut body having an axial length and a
substantially conical or tapered peripheral outer surface along a
substantial portion of said axial length; an outer annular collar
radially surrounding said nut body and having a complementary
conical or tapered recess to receive the cone nut body, in use; the
cone nut body being screwed, in use, on said studbolt and into the
recess of the outer annular collar, and adapted to be adjusted
along said studbolt and against said collar to take up elongation
of the studbolt as a result of applying tension to it; wherein,
said bridge stands directly upon said outer annular collar in
operation.
24. A washer for use between the cone nut body and article in the
tensioner as claimed in claim 23, the washer comprising: first and
second annular means mating at a slip plane angle from a plane
transverse to the axis of the washer; and removable or releasable
means holding the first and second annular means against relative
slip over the slip plane therebetween while the removable or
releasable means is in place.
Description
BACKGROUND OF THE INVENTION
1. Field of the Invention
THIS INVENTION relates to hydraulic systems for tensioning
fasteners; to nuts to be tensioned thereby; to tools to be used
therewith; to washers and to other like type structures and
accessories for use therewith.
2. Prior Art
Hydraulic nuts are known. The specification to Australian Patent
No. 625495 (AU-B-25403/88), to the present applicant, describes
such a nut. These nuts find applications in a variety of fields,
for example in the assembly of turbine casings.
Power industry turbine casings are invariably in two halves, joined
axially to make an essentially symmetric shell in which the turbine
rotor operates. The joint between the casings must be clamped with
sufficient force to withstand the massive forces of separation
generated by the action of steam under pressure within, and with a
high degree of consistency to prevent leakage or distortion of the
casing. Steam turbines operate of necessity at high temperatures,
so the nature of the material used in the bolts must resist creep
(slow relaxation) under such conditions. This rules out using
particularly high-strength heat treated alloy fasteners, so the
engineering solution taken is that of using studbolts of large
cross sectional area at reduced separation (bolt pitch). This
reduced separation means that there is very little working room
around the bolts. This creates problems in applying the high torque
necessary to provide required tensile load in the member. Most
turbine manufacturers have, therefore, opted to recommend a
practice of heat induced elongation and subsequent shrinkage of the
individual studs for casing bolt tensioning. This is an extremely
costly method in the amount of time consumed, and it also has
detrimental effects on the integrity of the fasteners.
There has been considerable pressure applied by power generation
utility companies to the manufacturers of the turbines to improve
the methods used in this area. An "outage" of a baseline generator,
in a nuclear plant for example, can cost a considerable sum (in
excess of four million dollars) per day. There are economic reasons
to improve performance. The utility companies are of the opinion
that permanently installed hydraulic fasteners are the ideal method
of force application for these studbolts. However, there are design
changes necessary to best fit such equipment requiring
manufacturers and regulatory body approvals, so they have requested
an interim step which would still allow the use of hydraulic
tensioning without major design change. Ideally, they would use
such equipment as tools which are removed after application, and
which do not require replacement of the studbolts themselves.
SUMMARY OF THE INVENTION
Following experience gained in the development of high temperature
hydraulic nuts for the power generation industry, the inventor
proposes herein solutions to inherent problems of tensioning
fasteners which are applied in circumstances offering limited
working geometries such as fasteners used in fixing turbine
casings.
It is an object of the present invention to provide one or more
improvements and developments which address the above issues. In
particular, a preferred object of the invention is to produce an
hydraulic bolt tensioner and accessories therefor which can apply
high tensile forces in very confined spaces. Various other objects
and particular advantages will hereinafter become apparent.
Throughout the specification, the term "studbolt" shall include
bolts and other fasteners.
The invention provides, in a first aspect, an hydraulic tensioner
for application with a studbolt fitted with a nut, said tensioner
having, including or comprising:
a puller bar for engagement in an internal thread with the
studbolt;
a puller buddy for engagement with an external thread on the
studbolt and with the puller bar, to work with an hydraulic means
acting via a bridge around and/or over a nut and against the puller
bar to tension the studbolt.
In a second aspect, the present invention resides in a hydraulic
tensioner for a studbolt or similar, fitted with a nut, extending
from an article or machine, said tensioner including or
comprising:
a puller bar for engagement in an internal thread in an end of the
studbolt;
a bridge extending around and/or over the nut, engageable with the
article or machine; and
hydraulic means between the puller bar and bridge and operable to
cause the puller bar to tension the studbolt by pulling the one end
of the studbolt in a direction away from the article or
machine.
Preferably, the hydraulic tensioner further includes a puller buddy
engageable with an external thread about the one end of the
studbolt and engageable with the puller bar.
Preferably, the internal thread in the studbolt is stepped in
diameter and the puller bar has a threaded end with complementary
stepped external threads.
Alternatively, the internal thread in the studbolt is substantially
conical or tapered; and
the puller bar has a thread end with a complementary substantially
conical or tapered external thread.
Preferably, the internal thread on the studbolt and the external
thread on the end of the puller bar are of tapered buttress
threads.
Preferably, the shoulders of the buttress threads are at an angle
of approximately 10.degree. (to the normal to the horizontal axes
of the studbolt and puller bar). i.e., the threaded end of the
puller bar has a 10.degree. taper.
Preferably, the pitch of the external thread on the puller bar is
greater than the pitch of the internal thread in the studbolt.
Preferably, the pitch of the external thread on the puller bar is
100.1% to 100.5% of the pitch of the vertical thread in the
studbolt.
Preferably, the pitch of the external thread on the puller bar is
3.005 mm; and the pitch of the vertical thread in the studbolt is
3.00 mm.
In a third aspect, the present invention resides in a coupling for
the hydraulic tensioner of the type as hereinbefore described
wherein:
the internal thread on the studbolt and the external thread on the
end of the puller bar are of tapered buttress threads.
Preferably, the shoulders of the buttress threads are at an angle
of approximately 10.degree. (to the normal to the horizontal axes
of the studbolt and puller bar).
Preferably, the pitch of the external thread on the puller bar is
greater than the pitch of the internal thread in the studbolt.
Preferably, the pitch of the external thread on the puller bar is
100.1% to 100.5% of the pitch of the vertical thread in the
studbolt.
Preferably, the pitch of the external thread on the puller bar is
3.005 mm; and the pitch of the vertical thread in the studbolt is
3.00 mm.
Preferably, the profile of the buttress type thread is that having
an exaggerated thread root radius.
In a fourth aspect, the invention further provides a nut with
particular attributes suited to working with the aforesaid
hydraulic tensioner having, including or comprising a nut body with
a substantially conical or tapered peripheral surface, an annular
shell with a complementary conical or tapered recess to receive the
nut body, in use, the nut body being screwed, in use, on a studbolt
into the recess of the annular shell.
In a fifth aspect, the present invention provides a nut assembly
for use with the hydraulic tensioner as hereinbefore described, the
nut assembly having, including or comprising:
a nut body with a substantially conical or tapered peripheral
surface;
an annular collar or shell with a complementary conical or tapered
recess to receive the nut body, in use; and
the nut body being screwed, in use, on the studbolt into the recess
of the annular collar or shell.
Preferably, the nut assembly further includes a base washer having
a substantially part-spherical face engageable by a complementary
part-spherical face on the annular collar or shell to enable the
base washer and annular collar or shell to be self-aligning.
The invention still further provides, in a sixth aspect, a washer
ideally suited for use with the aforesaid tensioner and/or conical
nut, said washer having, including or comprising first and second
annular means mating at a slip plane angled from the plane
transverse to the axis of the washer, and removable or releasable
means holding the first and second annular means against relative
slip over the slip plane therebetween whilst the removable or
releasable means is in place.
BRIEF DESCRIPTION OF THE DRAWINGS
The invention will now be described with reference to various
preferred embodiments, seen in greater detail in the accompanying
drawings in which:
FIG. 1 illustrates a prior art approach to tensioning a nut on a
studbolt;
FIGS. 2 and 3 are plan and vertical sectional views of a nut in
accordance with the invention;
FIG. 4 is a vertical section through an hydraulic tensioner mounted
to a nut of the kind seen in FIGS. 2 and 3;
FIG. 5 is a view of a detail in FIG. 4;
FIGS. 6 to 8 are vertical section, plan and sectional detail of
another hydraulic tensioner in accordance with the invention;
FIG. 9 is a view of one embodiment of a washer in accordance with
the invention;
FIGS. 10 to 12 are views of alternate embodiments of washers for
use with the invention;
FIGS. 13 to 16 show yet further embodiments for washers in
accordance with the invention;
FIGS. 17 and 18 show detailed views of mechanisms for rotating the
nuts employed in tensioning systems in accordance with the
invention;
FIGS. 19 to 24 show additional embodiments for washers in
accordance with the invention;
FIG. 25 is a vertical sectional view showing one embodiment of a
coupling between tensioning means and the studbolt;
FIG. 26 is a similar view of a second embodiment of a coupling;
FIG. 27 is a similar view of a third embodiment of a coupling;
FIG. 28 is a vertical elevational view of the puller bar of FIG.
27;
FIG. 29 is a vertical sectional view of a fourth embodiment of the
coupling;
FIG. 30 is a sectional view of the threads of the coupling, on an
enlarged scale; and
FIG. 31 is a sectional view showing the stress concentrations in
the coupling of FIG. 30.
DESCRIPTION OF THE PREFERRED EMBODIMENTS OF THE INVENTION
FIG. 1 illustrates a known approach to the above stated problem
which uses a bridge to go over the nut. The studbolt 10 is fitted
with a nut 11, fitted with a nut rotator 12, having holes enabling
engagement of the nut rotator which a suitable tool to turn it.
Above the nut 11 is an hydraulic assembly 13 comprising a piston
member 14, threadably engaged on stud 10 and extending down into a
cylinder member 15, the two members 14, 15 working together with an
expansion chamber therebetween, into which chamber may be charged
an hydraulic fluid under pressure (via charge port 16) the
expansion chamber being sealed at 17 in a manner known to those
skilled in the art. This type of structure is seen in the prior
Australian patent specification referred to above. The cylinder
member 15 of the hydraulic assembly is worked against a bridge 18,
standing over the nut 11. Expansion of the hydraulic assembly 13
expands the assembly, tensioning the studbolt 10 to allow the nut
rotator 12 to be rotated to tighten the nut. After the nut 11 is
screwed firmly against the face of the element being held by the
studbolt 10, the hydraulic pressure may be relieved and the
hydraulic assembly 13 can be removed from the studbolt 10, which
therefore remains in tension. Clearly, the dimensions of the
applied hydraulic assembly 13, in directions transverse to the
studbolt 10, will be limited by the degree of spacing between
neighbouring studbolts 10.
The prior art practice described above is mounted over the nut 11,
with a bridge 18 as illustrated, the bridge 18 allowing access for
rotation of the nut 11 within. Clearly, when there is little room
between adjacent studs 10 and nuts 11, the bridge 18 must be thin
walled, and it will apply high bearing stresses upon the joint face
when operating. In practice, the nuts 11 are so close as to almost
touch, which also means that the distance between the closest
interference and diameter of any studbolt 10 does not allow for
much annular area in the tensioner. Bolt tensioners have been
constructed which have required the use of an extended studbolt to
get above the spatial restrictions. If used as a replacement
fitting, then all the studbolts will have to be changed and the
turbine insulating covers altered at considerable cost of, in
typical circumstances, $1.5 to $2 million per machine.
The above studbolt is by definition of the same strength as
original equipment, so the connection with the bolt tensioner
therefore cannot be reduced in diameter to allow the bolt tensioner
tool to have more interior annular pressure area. This means that
the tensioner is required to have several load cells (in a stacked
configuration known to those skilled in the art) and even longer
stud length to accommodate same. The resulting tensioners made by
others in this area are therefore huge items requiring special
studs with modifications to the machine and cannot be used in close
proximity. They would interfere badly if used on consecutive
studs.
With the aforementioned in mind, the inventor has designed the
herein described hydraulic bolt tensioner and accessories which can
be produced in a form which is comparatively very small, yet still
provides high tensioning forces within the existing spotface
dimensions of turbine casings. As a consequence, these items may
therefore be used on every casing bolt simultaneously, which is a
massive boost to productivity. The inventor proposes a modification
to existing studbolts 10 to adapt them to this system. As best
practice, the inventor proposes to replace existing nuts 11 with a
companion development, a mechanical superior type nut 21 having
better thread load distribution characteristics. Another particular
development is a washer 24 by which the tension in a studbolt may
be relieved.
A nut 20 which is proposed below may be a three-part assembly,
being a fitted substantially cone shaped member 21, or equivalent;
and collar-like member 23, preferably resting on, typically, a
spherical base washer 24. In a preferred form (see below), the cone
nut 21 may have a gear 22 cut into its outer diameter to enable or
allow its rotation during tensioning (see, e.g., FIG. 18).
In FIGS. 2, 3 and 4, there is illustrated a development in
accordance with the present invention. The studbolt 19 may have an
external thread 19a to which can be applied a nut structure 20
incorporating the cone nut 21 and an hydraulic tensioning assembly
25 in accordance with the invention. The hydraulic assembly 25 may
involve multiple load cells, eg., three in this example numbered as
26, 27, 28, each with a respective piston and cylinder such as 29
and 30, as shown for load cell 26, and each with a charge port 31
in the case of load cell 26. (The charge ports 31 are connected to
a manifold 32.) The load cells 26, 27, 28 work upwardly against a
bar nut 34 on a tension transmitting member 33, hereinafter
referred to as a "puller bar", which extends downwardly, centrally
of the load cells 26 28 to (optionally) a threaded end 36 which may
screw-threadably engage a complementary bore in studbolt 19. The
puller bar 33 may have an engagement face or shoulder 35, acting
with or working against an intermediate load transmitting means,
hereinafter called a "puller buddy" 37, screw-threadably or
otherwise engaged to an external thread (in this example) on the
studbolt 19. Together, the puller bar 33 and puller buddy 37
co-operate to tension the studbolt 19. The hydraulic assembly 25
extends downwardly, past the cone nut 21, preferably via a bridge
38, which may sit atop the shell 23, acting or working thereby
against washer 24 in the process of tensioning the studbolt 19.
Elongation resulting from tensioning of the studbolt 19 by action
of the tensioning assembly 25 on the studbolt 19 can be taken up by
rotation of the cone nut 21.
The above illustrates the means by which high tensile loads may be
applied without damaging the threads 19a of engagement of the
studbolt 19, or exceeding the spotface dimensions allowable for
each size. A tensioner assembly 25 manufactured as illustrated may
produce a tensile force of 50 tons/in.sup.2 on a 2'' Studbolt. The
arrangement shown allows the load applied by the puller bar 33 on
the inner threads 19b of the studbolt 19, and the load applied by
the puller buddy 37 on the outer threads 19a to be distributed
between the respective threads of engagement during tensioning. The
force which can be delivered may only be limited by the tensile
strength of that sectional area of the studbolt 19 which is subject
to said force. This can be maximised by manipulating the actual
point of application of load via inner and outer threads 19b, 19a.
For example, if the inner bar were shorter as illustrated and the
puller buddy 37 picked up load in full thickness of the studbolt 19
as per the illustration, full load can then be distributed across
the section in a very favourable manner.
FIG. 5 shows the studbolt 19, puller bar 33 and puller buddy 37 of
FIG. 4. The relative extent of the thread of the threaded end 36 of
the puller bar 33, in the inner threads 19b of the studbolt 19, and
the puller buddy 37 on the outer threads 19a of the studbolt, can
be arranged to produce load concentrations 39, 40, as discussed
above.
The inventor has also designed variations of the puller/buddy
tensioner which do not rely on the use of the cone type nut. As
illustrated (see discussion below), the operative strength of a hex
nut is governed by its minimum wall thickness. The proposal here
can make use of the difference in Across Flats and Across Corners
dimensions of hex nuts to mount a bridge directly onto a modified
spherical washer at full spotface dimensions. There may be
sufficient stud protrusion above the joint to fit a Ring Nut, and
after tensioning is complete, a Cap Nut can be screwed onto the top
to protect the thread.
FIGS. 6 to 8 show an assembly of the kind in FIG. 4 applied to a
system not using a cone nut. In this embodiment, a studbolt 41 is
fitted with a nut 42 with an hydraulic assembly 43 (equivalent to
hydraulic assembly 25 of FIG. 4) to tension the stud 41 via a
puller 44 and a buddy 45. The assembly 43 acts down via bridge 47
to washer 48. The assembly 43 may be removed after tensioning and
tightening of the nut 42 with the exposed end of the stud 41 as
seen in FIG. 8 fitted with a protective cap (not shown). The nut 42
is a round nut of just sufficient thickness to hold the load. In
FIG. 7 is seen the round nut 42 with its equivalent hex nut shown
in dotted outline. There is a saving in overall diameter by moving
away from the hex nut structure leading to more room to work with
when applying tensioners to studbolts.
As part of a total package for Turbine Tensioning Systems the
inventor has developed a device designed to replace the torch ring
often used where it is considered quicker to release clamp force by
cutting and removing a piece of the assembly. It is difficult to
advocate the use of sacrificial parts and oxy cutting thereof
around multi-million dollar hardware, so the inventor proposes the
use of a "friction washer" 51 which can be released
voluntarily.
FIG. 9 illustrates a friction washer in accordance with the
invention. The washer 51 is in two parts or halves 52, 53, mated
across sloped surfaces at line 54. The two parts 52, 53 held in
position by bolts 55 in holes 56 and threads (not shown) in part
52. When a nut is to be released, the bolts 55 may be removed and a
tap with a hammer can cause slip over plane 54 to release tension.
The friction washer 51 is loaded by the compressive force applied
to the joint and two halves 52, 53 are held together by friction.
The degree of slope is chosen to enable slip when the washer 51 is
given a jolt after the retaining bolts or the wedges (see below)
are removed.
The above friction washer 51 is a simple yet effective device in
which the friction between the opposing faces holds the washer
together as a function of the force exerted downwards by the bolt
tension. As the relationship is essentially linear, then the
correct slip plane angle can be determined from those inherent
factors and the co-efficient of friction of the base material. It
is set so that when the bolt is under tension, the capscrews will
provide force just sufficient to hold the assembly together. Remove
the capscrews, and apply a light blow to overcome sticking
friction, and the washer separates along the slip plane. Design of
the washer can be varied.
In FIGS. 10 to 12 are shown variations of the slip washer of FIG.
9. In FIGS. 10 and 11, the two parts are held by keys 57, 58 or
small wedges which may be removed to allow slip of the two
sections. In FIG. 12, the slip plane is stepped at 59 to allow easy
assembly with bolts fed into holes such as 60 extended through the
shoulder. For those with lingering doubts about removal of bolts
under high tensile load, then these offer great reassurance. In
practice, there may be so much removal time saved that they could
become valuable in applications not utilising the other features of
the presently set out system.
FIG. 13 illustrates a plan view of a washer fitted with an annular
locking ring 62. The washer may be formed in a number of sections
meeting at slip planes and three are seen in the drawing. The
washer and ring is shown in transverse section in FIG. 14. In FIG.
14, the washer is a three part construction with sections 61, 63,
and 64 mating together at opposed sloping slip planes. The locking
ring 62 holds the assembly together during installation. The
locking ring 62 can be removed to enable displacement of the
sections. In FIGS. 15 and 16 is shown a three part assembly in
which the washer sections 67, 68 and 69 are held together by wedges
65, 66.
FIG. 17 shows in detail where a cone nut 70, on a studbolt 71, is
turned by means of a tommy bar 74 engaged in a hole such as 75 via
slot 73 in bridge 72. A variation is shown in FIG. 18. In FIG. 18,
the cone nut 70 is rotated by a gear assembly 76, with gear 77
engaged with a cone nut 70. The gear assembly 76 is rotated by
application of a suitable driver at 78.
In FIGS. 19 to 24 are illustrated variations of the above described
washers, wherein a lock ring 79, 85 holds segment pieces such as 80
which together act as a washer. Removal of the locking ring 79
releases them to release the load. The segment piece 81 of FIG. 20
may have a conical face 82. The piece 83 of FIG. 24 is formed with
a flat face 84 which come together with locking ring 85 to form the
assembly of FIG. 22.
FIG. 25 shows an hydraulic arrangement where the hydraulic tension
system 125 (corresponding to the system 25 of FIG. 4) has a puller
bar 133/puller buddy 137 combination where there is no reduction in
the diameter of the external threads 119a on the studbolt 119, the
latter being fitted with a cone nut assembly 120.
In FIG. 26, the puller bar 133/puller buddy 137 of the hydraulic
tension system 225 co-operates with stud bolt 219 where the
external threads 219a on the studbolt 219 are of reduced
diameter.
FIG. 27 shows a hydraulic tensioning system 325, where the puller
bar 333 has a threaded end 336 divided into respective stepped
diameter zones 336a and 336b (in the direction away from the
abutment 335) to engage the internal threads 319b in a stepped bore
in the studbolt 319. A puller buddy 337 is engaged with the
external threads 319a on the studbolt.
FIG. 29 shows a more preferred coupling arrangement between the
puller bar 433 (of the hydraulic tension system 425) and the
studbolt 419, where the respective threads 436a (on the puller bar
433) and 419b (in the studbolt 419) are of complementary
(substantially) conical configuration, as shown in enlarged scale
in FIG. 30.
The hydraulic tensioning systems 225, 325, 425 correspond to the
hydraulic tension system 225 of FIG. 4 and operate in like
manner.
The inventor has examined various threaded connections for the
tensioner/studbolt interface, and found that the simplest
configuration having the best stress distribution is a 100 tapered
buttress thread modelled on the standard API cone thread. Tapered
cone styles with 60.degree. threads have been around as connectors
for tensile rods such as drill steels since the industrial
revolution--downhole hammers used in drilling have a modified
tapered buttress thread form, as do components of rock crushing
equipment. The specific benefits of using this type of thread are
resistance to loosening, quick breakout and the use of thin walled
elements as the threadform does not generate significant radial
thrust forces. The inventor has chosen to use a modified buttress
with a slight overpitch (increased thread pitch) (eg., 3.005 mm) on
the puller (relative to 3.00 mm on the studbolt) which gives a
near-perfect load distribution on the threads. The shoulders of the
buttress-form threads are essentially perpendicular to the pullers
and bolts common axis, and therefore have no radial thrust.
The inventor has designed a specific threadform for this
application, as shown in FIG. 30. It has a very low face angle
(eg., 2.5.degree.) and exaggerated root radii (eg., 0.2 0.25 mm) to
prevent stress concentrations common with generic forms. The more
even stress concentration patterns in the components are
illustrated by the stress concentration pattern shown in FIG.
31.
The cone nut assembly 20 can be specifically designed using
computer modelling to obtain the best possible component shape to:
1. retain the highest proportion of load provided by the hydraulic
mechanism when transferring that load to the nut assembly; 2.
provide even loading of the threaded interface rather than the
concentration of load found with standard nut/bolt connections.
This is preferably achieved by modelling the components'
deflections during the complete operational cycle of the tensioner
to determine the precise set of dimensions "pre-tensioning" which
will give the ideal deflected shape "post tensioning". Obviously,
the shape of various sections of components will alter during
cycle, and the designer must know what shape to make them so that
their compressed shape will allow optimised performance of the
fasteners.
The operation of the "cone nut" assembly 20 is quite complex. After
being screwed into position during hydraulic pump-up phase, when
the pressure is relieved from the system, the upper nut part 21
(with internal cone face) is first put into tension, simply hanging
off the upper face of engagement with the collar or cone outer 23.
Then, as pressure relief continues, the load being transferred to
the "cone nut" assembly 20 increases, the lower part of the thread
radially deflects progressively upwards and contacts the adjacent
tapered face of the collar. This action effectively dissipates the
concentrations of load throughout the thread contact zone,
therefore, limiting the radial thrust factor and associated losses
of tensile load and bolt extension in the system.
The invention has been described with respect to preferred
arrangements which relate to a task where it has ideal application.
The scope of the invention is not limited to the embodiments and
use hereto described, but also to a wide range of other
applications which would be clear to those skilled in the art. Some
examples would be for valves, flanges, pumps, compressors, engines
and pressure vessels where components of such equipment are
retained by tensile members.
* * * * *